AU2021386726A1

AU2021386726A1 - Flow path switching device and method for preventing dry running of submerged-type pump

Info

Publication number: AU2021386726A1
Application number: AU2021386726A
Authority: AU
Inventors: Shuichiro Honda; Hayato Ikeda; Mitsutaka IWAMI; Tetsuji KASATANI
Original assignee: Ebara Corp
Current assignee: Ebara Corp
Priority date: 2020-11-27
Filing date: 2021-08-27
Publication date: 2023-06-29
Also published as: WO2022113450A1; CA3202585A1; US20240011492A1; EP4253759A1; AU2021386726A9; CN116529489A; JPWO2022113450A1; KR20230107360A

Abstract

The present invention relates to technology for preventing dry running of a submerged-type pump used for transferring liquefied gas such as liquefied ammonia, liquid hydrogen, liquid nitrogen, liquefied natural gas, liquefied ethylene gas, and liquefied petroleum gas. A flow path switching device (5) comprises a flow path structure (45) that has a first flow path (41), a second flow path (42), and a third flow path (43), and a valve (47) that is disposed in the flow path structure (45) and that selectively connects the third flow path (43) to the first flow path (41) or the second flow path (42), wherein the first flow path (41) is connected to a discharge opening (1b) of the submerged-type pump (1), the second flow path (42) is connected to the inside of an intake container (2), and the third flow path (43) is connected to a discharge port (8) of the intake container (2).

Description

DESCRIPTION

Title of Invention

FLUID-PATH SWITCHING APPARATUS AND METHOD OF PREVENTING IDLING ROTATION OF SUBMERSIBLE PUMP

Technical Field

[0001] The present invention relates to a technique of preventing idling rotation of a

submersible pump used for delivering liquefied gas, such as liquefied ammonia, liquid

hydrogen, liquid nitrogen, liquefied natural gas, liquefied ethylene gas, or liquefied

petroleum gas.

Background Art

[0002] Natural gas is widely used for thermal power generation and as a raw material

for chemicals. Furthermore, ammonia and hydrogen are expected to be energies that do

not generate carbon dioxide that causes global warming. Applications of hydrogen as an

energy include fuel cell and turbine power generation. Natural gas, ammonia, and

hydrogen are in a gaseous state at normal temperature, and therefore natural gas,

ammonia, and hydrogen are cooled and liquefied for their storage and transportation.

Liquefied gas, such as liquefied natural gas (LNG), liquefied ammonia, and liquefied

hydrogen, is temporarily stored in a liquefied-gas storage tank and then delivered to a

power plant, factory, or the like by a pump.

[0003] FIG. 12 is a schematic diagram showing a conventional example of a pump

system for pumping up liquefied gas. A pump 500 is installed in a vertical suction

vessel 505, which is coupled to a liquefied-gas storage tank (not shown) in which the

liquefied gas is stored. The liquefied gas is introduced into the suction vessel 505

through a suction port 501, and the suction vessel 505 is filled with the liquefied gas.

The entire pump 500 is immersed in the liquefied gas. Therefore, the pump 500 is a

submersible pump that can operate in the liquefied gas. When the pump 500 is operated,

the liquefied gas is discharged by the pump 500 through a discharge port 502. During the operation of the pump 500, a part of the liquefied gas in the suction vessel 505 vaporizes into gas, which is exhausted from the suction vessel 505 through a vent line 503.

[0004] Before the pump 500 is operated, a drying-up operation of purging air out from

the suction vessel 505 with purge gas and a cooling-down operation of cooling the pump

500 with liquefied gas are performed. If the air present in the suction vessel 505 comes

into contact with the ultra-low temperature liquefied gas, moisture in the air is cooled and

solidified by the liquefied gas, which may impede the rotation of the pump 500.

Furthermore, if the pump 500 is at a normal temperature when the pump 500 is started,

the ultra-low temperature liquefied gas will vaporize when the liquefied gas contacts the

pump 500. In order to prevent such events, the drying-up operation and the cooling

down operation are performed before the pump 500 is operated.

[0005] The drying-up operation includes injecting a purge gas (e.g., nitrogen gas) into

the suction vessel 505, and the cooling-down operation includes injecting a liquefied gas

(e.g., liquefied natural gas) into the suction vessel 505. The purge gas or the liquefied

gas injected into the suction vessel 505 fills the suction vessel 505, flows into the pump

500 through an inlet 500a of the pump 500, and is discharged through the discharge port

502.

Citation List

Patent Literature

[0006] Patent document 1: Japanese laid-open utility model publication No. S59-159795

Patent document 2: Japanese examined utility model publication No. S62

031680

Summary of Invention

Technical Problem

[0007] However, the purge gas that has been supplied into the suction vessel 505 for the

drying-up operation flows through the pump 500 and may cause idling rotation (or free

rotation) of the pump 500. When the pump 500 is forced to idle by the purge gas,

sliding parts, such as bearings, may be damaged. Furthermore, the liquefied gas that has been supplied into the suction vessel 505 for the cooling-down operation comes into contact with the normal-temperature pump 500, thus forming a large amount of gas.

This gas may cause idling rotation of an impeller of the pump 500, which may cause

damage to sliding parts, such as bearings.

[0008] Accordingly, the present invention provides a fluid-path switching apparatus

capable of preventing idling rotation of a pump due to gas introduced into a suction vessel

for the purpose of a drying-up operation or a cooling-down operation for the pump. The

present invention also provides a method of preventing idling rotation of a submersible

pump. Solution to Problem

[0009] In an embodiment, there is provided a fluid-path switching apparatus for

preventing idling rotation of a submersible pump disposed in a suction vessel and used for

delivering liquefied gas, comprising: a flow-passage structure having a first flow passage,

a second flow passage, and a third flow passage; and a valve element arranged in the

flow-passage structure, the valve element being configured to allow the third flow

passage to selectively communicate with either the first flow passage or the second flow

passage, the first flow passage communicating with a discharge outlet of the submersible

pump, the second flow passage communicating with an interior of the suction vessel, and

the third flow passage communicating with a discharge port of the suction vessel.

[0010] In an embodiment, the flow-passage structure further includes a bypass passage

that establishes fluid communication between the first flow passage and the third flow

passage, and the bypass passage has a cross-sectional area smaller than a cross-sectional

area of the first flow passage.

In an embodiment, the cross-sectional area of the bypass passage is such that an

impeller of the submersible pump does not rotate due to flow of gas when the valve

element closes the first flow passage and the gas flows through the submersible pump and

the bypass passage.

In an embodiment, the fluid-path switching apparatus further comprises a spring configured to press the valve element against the flow-passage structure to close the first flow passage.

[0011] In an embodiment, there is provided a pump system comprising: a submersible

pump configured to deliver liquefied gas; a suction vessel in which the submersible pump

is accommodated; and the fluid-path switching apparatus for preventing idling rotation of

the submersible pump.

In an embodiment, the pump system further comprises a rotation detector

configured to detect rotation of the submersible pump.

In an embodiment, the pump system further comprises an anti-rotation device

configured to prevent rotation of the submersible pump.

[0012] In an embodiment, there is provided a method of preventing idling rotation of a

submersible pump disposed in a suction vessel and used for delivering liquefied gas,

comprising: supplying liquefied gas into the suction vessel when a first flow passage is

closed with a valve element, and a second flow passage and a third flow passage are in

fluid communication, the first flow passage communicating with a discharge outlet of the

submersible pump, the second flow passage communicating with an interior of the suction

vessel, the third flow passage communicating with a discharge port of the suction vessel;

and delivering gas generated in the suction vessel to the discharge port through the second

flow passage and the third flow passage.

[0013] In an embodiment, the method further comprises supplying purge gas into the

suction vessel before supplying the liquefied gas into the suction vessel.

In an embodiment, the purge gas is supplied into the suction vessel through a

suction port of the suction vessel and discharged through a drain line coupled to a bottom

of the suction vessel, the suction port being located higher than the bottom of the suction

vessel.

In an embodiment, the purge gas is supplied into the suction vessel through a

suction port of the suction vessel and discharged through the second flow passage, the

third flow passage, and the discharge port.

In an embodiment, the purge gas is supplied into the suction vessel through a

drain line coupled to a bottom of the suction vessel and discharged through the second

flow passage, the third flow passage, and the discharge port.

In an embodiment, the purge gas is an inert gas composed of element having a

boiling point lower than that of an element constituting the liquefied gas.

In an embodiment, the method further comprises operating the submersible

pump in a state in which the second flow passage is closed by the valve element and the

first flow passage communicates with the third flow passage.

In an embodiment, the method further comprises directing gas generated in the

suction vessel through the discharge port to a gas treatment device.

Advantageous Effects of Invention

[0014] According to the present invention, gas (e.g., purge gas, or gas generated from

liquefied gas, etc.) that has been introduced into the suction vessel during a drying-up

operation or a cooling-down operation does not flow into the submersible pump because

of the fluid-path switching apparatus, so that the gas is led to the discharge port.

Therefore, the impeller of the submersible pump is not forced to idle (or rotate freely),

and as a result, damage to sliding parts, such as bearings of the submersible pump, can be

prevented.

Brief Description of Drawings

[0015]

[FIG. 1] FIG. 1 shows an embodiment of a pump system for delivering liquefied gas;

[FIG. 2] FIG. 2 is a cross-sectional view showing an embodiment of detailed

configurations of a fluid-path switching apparatus;

[FIG. 3] FIG. 3 shows a state of the fluid-path switching apparatus when a submersible

pump is in operation;

[FIG. 4] FIG. 4 is a diagram for explaining an embodiment of a drying-up operation;

[FIG. 5] FIG. 5 is a diagram for explaining another embodiment of the drying-up operation;

[FIG. 6] FIG. 6 is a diagram for explaining still another embodiment of the drying-up

operation;

[FIG. 7] FIG. 7 is a diagram for explaining an embodiment of a cooling-down operation;

[FIG. 8] FIG. 8 is a diagram for explaining an embodiment of simultaneously cooling a

plurality of submersible pumps;

[FIG. 9] FIG. 9 is a cross-sectional view showing another embodiment of the fluid-path

switching apparatus;

[FIG. 10] FIG. 10 shows an embodiment of a pump system including a rotation detector;

[FIG. 11] FIG. 11 shows an embodiment of a pump system including an anti-rotation

device; and

[FIG. 12] FIG. 12 is a schematic diagram showing a conventional example of a pump

system for pumping up liquefied gas.

Description of Embodiments

[0016] Hereinafter, embodiments of the present invention will be described with

reference to the drawings. FIG. 1 illustrates an embodiment of a pump system for

delivering liquefied gas. Examples of the liquefied gas to be delivered by the pump

system shown in FIG. 1 include liquefied ammonia, liquid hydrogen, liquid nitrogen,

liquefied natural gas, liquefied ethylene gas, liquefied petroleum gas, and the like.

[0017] As shown in FIG. 1, the pump system includes a submersible pump 1 for

delivering the liquefied gas, a suction vessel 2 in which the submersible pump 1 is

accommodated, and a fluid-path switching apparatus 5 for preventing idling rotation of

the submersible pump 1. The suction vessel 2 has a suction port 7 and a discharge port 8.

The liquefied gas is introduced through the suction port 7 into the suction vessel 2, and an

interior of the suction vessel 2 is filled with the liquefied gas. During operation of the

submersible pump 1, the entire submersible pump 1 is immersed in the liquefied gas.

Therefore, the submersible pump 1 is configured to be operable in the liquefied gas.

[0018] The submersible pump 1 includes an electric motor 11 having a motor rotor 11A

and a motor stator 1IB, a rotation shaft 12 coupled to the electric motor 11, bearings 14A,

14B, and 14C that rotatably support the rotation shaft 12, an impeller 15 secured to the

rotation shaft 12, and a pump casing 16 in which the impeller 15 is housed. The fluid

path switching apparatus 5 is arranged in the suction vessel 2. More specifically, the

fluid-path switching apparatus 5 is coupled to both a discharge outlet lb of the

submersible pump 1 and the discharge port 8 of the suction vessel 2. Specific

configurations of the fluid-path switching apparatus 5 will be described later.

[0019] When electric power is supplied to the electric motor 11 through a power cable

(not shown), the electric motor 11 rotates the rotation shaft 12 and the impeller 15

together. As the impeller 15 rotates, the liquefied gas is sucked into the submersible

pump 1 through a suction inlet la of the submersible pump 1, flows through a discharge

flow passage 17 and the discharge outlet 1b, and is discharged into the fluid-path

switching apparatus 5. Further, the liquefied gas flows through the fluid-path switching

apparatus 5 into the discharge port 8 of the suction vessel 2. A discharge pipe 20 is

coupled to the discharge port 8, so that the liquefied gas that has flowed through the

discharge port 8 is delivered through the discharge pipe 20.

[0020] A suction valve 22 is coupled to the suction port 7, and a discharge valve 23 is

coupled to the discharge port 8. A drain line 25 is coupled to a bottom of the suction

vessel 2, and a drain valve 26 is coupled to the drain line 25. The suction port 7 is

provided on a side wall of the suction vessel 2 and is located higher than the bottom of the

suction vessel 2. The discharge port 8 is provided on an upper portion of the suction

vessel 2 and is located higher than the suction port 7. During operation of the

submersible pump 1, the suction valve 22 and the discharge valve 23 are open, and the

drain valve 26 is closed. A vent line 31 is coupled to the upper portion of the suction

vessel 2. During operation of the submersible pump 1, a part of the liquefied gas

evaporates into gas due to heat generation of the submersible pump 1. This gas is

discharged from the suction vessel 2 through the vent line 31. A vent valve 32 is coupled to the vent line 31. In one embodiment, this gas may be delivered through the vent line 31 to a gas treatment device (not shown). The gas treatment device is configured to treat the gas (e.g., natural gas, hydrogen gas, or ammonia gas) vaporized from the liquefied gas. Examples of the gas treatment device include gas incinerator

(flaring device), chemical gas treatment device, gas adsorption device, and the like.

[0021] FIG. 2 is a cross-sectional view showing an embodiment of detailed

configurations of the fluid-path switching apparatus 5. As shown in FIG. 2, the fluid

path switching apparatus 5 includes a flow-passage structure 45 having a first flow

passage 41, a second flow passage 42, and a third flow passage 43, and a valve element

47 arranged in the flow-passage structure 45. The first flow passage 41 communicates

with the discharge outlet lb of the submersible pump 1, the second flow passage 42 communicates with the interior of the suction vessel 2, and the third flow passage 43

communicates with the discharge port 8 of the suction vessel 2. The valve element 47 is

arranged so as to allow the third flow passage 43 to selectively communicate with either

the first flow passage 41 or the second flow passage 42. The configurations of the fluid

path switching apparatus 5 are not limited to the embodiment shown in FIG. 2 as long as

its intended function can be achieved.

[0022] FIG. 2 shows a state of the fluid-path switching apparatus 5 when the submersible pump 1 is not in operation. The valve element 47 is pressed against the

flow-passage structure 45 by a spring 50 to thereby close the first flow passage 41.

More specifically, the flow-passage structure 45 has a valve seat 51 formed around an

outlet of the first flow passage 41, and the valve element 47 is pressed against the valve

seat 51 by the spring 50. Therefore, when the valve element 47 is pressed against the

valve seat 51, the first flow passage 41 is closed, while the second flow passage 42 and

the third flow passage 43 are in fluid communication. The second flow passage 42 is

open in the suction vessel 2 and communicates with the suction port 7 through the interior

of the suction vessel 2.

[0023] FIG. 3 shows a state of the fluid-path switching apparatus 5 when the submersible pump 1 is in operation. When the submersible pump 1 is in operation, the liquefied gas is discharged from the discharge outlet lb of the submersible pump 1 and flows into the first flow passage 41 of the fluid-path switching apparatus 5. The liquefied gas flowing through the first flow passage 41 moves the valve element 47 against the force of the spring 50 to open the first flow passage 41 and close the second flow passage 42 with the valve element 47. As a result, the first flow passage 41 and the third flow passage 43 communicate with each other.

[0024] When the operation of the submersible pump 1 is stopped, the valve element 47

is pressed against the valve seat 51 by the spring 50. As a result, as shown in FIG. 2, the

first flow passage 41 is closed, and the second flow passage 42 and the third flow passage

43 communicate with each other. In this manner, the fluid-path switching apparatus 5 of

this embodiment operates only by the spring 50 and the flow of the liquefied gas. In one

embodiment, the fluid-path switching apparatus 5 may have an actuator (for example, an

electrical actuator or a hydraulic actuator) configured to move the valve element 47.

[0025] Before the operation of the submersible pump 1 is started, a drying-up operation

is performed which is to remove air from the suction vessel 2 with purge gas, and a

cooling-down operation is performed which is to cool the submersible pump 1 with the

liquefied gas. The drying-up operation and the cooling-down operation are performed

in the state shown in FIG. 2, i.e., in the state in which thefirst flow passage 41 is closed

with the valve element 47, and the second flow passage 42 and the third flow passage 43

are in fluid communication.

[0026] The drying-up operation is an operation of introducing purge gas having a

normal temperature into the suction vessel 2 to dry the submersible pump 1. An

embodiment of the drying-up operation will be described below with reference to FIG. 4.

The purge gas is delivered through the suction port 7 into the suction vessel 2 while the

submersible pump 1 is not in operation (i.e., the state shown in FIG. 2). The discharge

valve 23 and the vent valve 32 are closed, and the suction valve 22 and the drain valve 26

are open. The vent valve 32 may be open. The purge gas purges the air present in the suction vessel 2 and is discharged together with the air through the drain line 25. The interior of the suction vessel 2 is filled with the purge gas, which dries the submersible pump 1.

[0027] In one embodiment, the drying-up operation may be performed as follows. As

shown in FIG. 5, when the submersible pump 1 is not in operation (i.e., the state shown in

FIG. 2), the purge gas is delivered through the suction port 7 into the suction vessel 2.

The drain valve 26 and the vent valve 32 are closed, and the suction valve 22 and the

discharge valve 23 are open. The vent valve 32 may be open. The purge gas purges

the air present in the suction vessel 2 and is discharged together with the air through the

second flow passage 42 and the third flow passage 43 of the fluid-path switching

apparatus 5 and the discharge port 8. The interior of the suction vessel 2 is filled with

the purge gas, which dries the submersible pump 1.

[0028] Furthermore, in one embodiment, the drying-up operation may be performed as

follows. As shown in FIG. 6, when the submersible pump 1 is not in operation (i.e., the

state shown in FIG. 2), the purge gas is delivered through the drain line 25 into the

suction vessel 2. The suction valve 22 and the vent valve 32 are closed, and the drain

valve 26 and the discharge valve 23 are open. The vent valve 32 may be open. The

purge gas purges the air present in the suction vessel 2 and is discharged together with the

air through the second flow passage 42 and the third flow passage 43 of the fluid-path

switching apparatus 5 and the discharge port 8. The interior of the suction vessel 2 is

filled with the purge gas, which dries the submersible pump 1.

[0029] In the embodiments shown in FIGS. 4 to 6, the first flow passage 41 is closed by

the valve element 47. Therefore, the purge gas introduced into the suction vessel 2 does

not flow through the submersible pump 1. As a result, idling rotation of the impeller 15

of the submersible pump 1 is prevented, and sliding parts, such as the bearings 14A, 14B,

14C, are prevented from being damaged.

[0030] The purge gas used for the drying-up operation is an inert gas composed of

element having a boiling point lower than that of an element constituting the liquefied gas.

This is to prevent the purge gas from being liquefied when the purge gas comes into

contact with the cryogenic liquefied gas introduced after the drying-up operation. For

example, if the liquefied gas is liquefied natural gas (LNG) or liquefied ammonia, the

purge gas used is nitrogen gas. In another example, if the liquefied gas is liquid

hydrogen, the purge gas used is helium gas.

[0031] The cooling-down operation is an operation of introducing the liquefied gas into

the suction vessel 2 to cool the submersible pump 1 after the drying-up operation. An

embodiment of the cooling-down operation will be described below with reference to FIG.

7. As shown in FIG. 7, when the submersible pump 1 is not in operation (i.e., the state

shown in FIG. 2), the liquefied gas is delivered through the suction port 7 into the suction

vessel 2. The drain valve 26 and the vent valve 32 are closed, and the suction valve 22

and the discharge valve 23 are open. The vent valve 32 may be open. The liquefied

gas comes into contact with the submersible pump 1 and the suction vessel 2 each having

a normal temperature and vaporizes to generate gas (hereinafter referred to as generated

gas). The generated gas is discharged through the second flow passage 42 and the third

flow passage 43 of the fluid-path switching apparatus 5 and the discharge port 8. As the

temperatures of the submersible pump 1 and the suction vessel 2 decrease, the liquefied

gas will no longer vaporize. The interior of the suction vessel 2 is filled with the

liquefied gas, which cools the submersible pump 1.

[0032] The first flow passage 41 is closed by the valve element 47 in the embodiment of

FIG. 7. Therefore, the generated gas in the suction vessel 2 does not flow through the

submersible pump 1. As a result, the idling rotation of the impeller 15 of the

submersible pump 1 is prevented, and the sliding parts, such as the bearings 14A, 14B,

14C, are prevented from being damaged.

[0033] As shown in FIG. 7, the generated gas is discharged through the discharge port 8

and the discharge pipe 20. The discharge port 8 and the discharge pipe 20 typically have

a larger diameter than those of the vent line 31 and the drain line 25. Therefore, the

liquefied gas for cooling the submersible pump 1 can be introduced into the suction vessel

2 at a high flow rate. As a result, the cooling-down operation can be completed in a

short time. In particular, according to the present embodiment, even if the liquefied gas

is introduced into the suction vessel 2 at a high flow rate, the fluid-path switching

apparatus 5 prevents the generated gas (gas generated as a result of vaporization of the

liquefied gas) from flowing through the submersible pump 1 and can therefore prevent the

idling rotation of the submersible pump 1.

[0034] In one embodiment, the generated gas in the suction vessel 2 may be directed

through the discharge port 8 and the discharge pipe 20 to a gas treatment device (not

shown). The gas treatment device is configured to treat the gas (e.g., natural gas,

hydrogen gas, or ammonia gas) vaporized from the liquefied gas. Examples of the gas

treatment device include gas incinerator (flaring device), chemical gas treatment device,

gas adsorption device, and the like.

[0035] As shown in FIG. 8, it is possible to couple a plurality of suction vessels 2 in

series to cool a plurality of submersible pumps 1 simultaneously. Specifically, a

discharge port 8 of one suction vessel 2 accommodating one submersible pump 1 is

coupled to a suction port 7 of another suction vessel 2 accommodating another

submersible pump 1. Three or more suction vessels 2 can be coupled in series in the

same way. The liquefied gas is introduced into a suction port 7 of one of the plurality of

suction vessels 2, flows through each suction vessel 2 and is discharged from a discharge

port 8 of another of the plurality of suction vessels 2. The liquefied gas flowing through

these suction vessels 2 can cool the multiple submersible pumps 1 simultaneously.

[0036] FIG. 9 is a cross-sectional view showing another embodiment of the fluid-path

switching apparatus 5. Configurations and operations of this embodiment, which will

not be specifically described, are the same as those of the embodiments described with

reference to FIGS. 2 and 3, and their repetitive descriptions will be omitted. As shown

in FIG. 9, the flow-passage structure 45 has a bypass passage 55 that establishes fluid

communication between the first flow passage 41 and the third flow passage 43. The

bypass passage 55 has a cross-sectional area smaller than a cross-sectional area of the first flow passage 41. More specifically, the cross-sectional area of the bypass passage 55 is such that the rotation of the impeller 15 of the submersible pump 1 due to the gas flow does not occur when the valve element 47 closes the first flow passage 41 and the gas (the purge gas or the generated gas) flows through the submersible pump 1 and the bypass passage 55.

[0037] The bypass passage 55 may be a through-hole as shown in FIG. 9 or may be a

groove formed in the valve seat 51. A plurality of bypass passages 55 may be provided

as long as the above-described gas does not cause the rotation of the impeller 15.

According to this embodiment, the purge gas or the liquefied gas can be smoothly

introduced into the submersible pump 1 during the drying-up operation and the cooling

down operation. As a result, the drying-up operation and the cooling-down operation for

the submersible pump 1 can be completed in a shorter time.

[0038] As shown in FIG. 10, in one embodiment the pump system may include a

rotation detector 60 configured to detect the rotation of the submersible pump 1. A

specific configuration of the rotation detector 60 is not particularly limited as long as the

rotation detector 60 can detect the rotation of the submersible pump 1 (i.e., the rotation of

the rotation shaft 12 or the impeller 15). In the example shown in FIG. 10, the rotation

detector 60 is an induced electromotive force detector configured to detect an induced

electromotive force generated when the electric motor 11 is rotating. In another

example, although not shown, the rotation detector 60 may be configured to directly

detect the rotation of the rotation shaft 12 or the impeller 15. Based on an output value

of the rotation detector 60, the cross-sectional area of the bypass passage 55 that does not

cause the rotation of the submersible pump 1 can be determined.

[0039] As shown in FIG. 11, in one embodiment, the pump system may further include

an anti-rotation device 70 configured to prevent the rotation of the submersible pump 1.

A specific configuration of the anti-rotation device 70 is not particularly limited as long

as the anti-rotation device 70 can prevent the rotation of the submersible pump 1 (i.e.,

rotation of the rotation shaft 12 or the impeller 15). For example, the anti-rotation device 70 may be a mechanical anti-rotation device configured to press a brake pad against the rotation shaft 12 to prevent the rotation of the rotation shaft 12 and the impeller 15. Examples of actuator that moves the brake pad include a hydraulic actuator

(e.g., a gas cylinder), an electrical actuator (e.g., an electromagnetic solenoid), and the

like. In another example, the anti-rotation device 70 may be an electromagnetic anti

rotation device configured to energize a coil to generate an electromagnetic force that

prevents the rotation of the rotation shaft 12 and the impeller 15.

[0040] The previous description of embodiments is provided to enable a person skilled

in the art to make and use the present invention. Moreover, various modifications to

these embodiments will be readily apparent to those skilled in the art, and the generic

principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments

described herein but is to be accorded the widest scope as defined by limitation of the

claims.

Industrial Applicability

[0041] The present invention is applicable to a technique of preventing idling rotation of

a submersible pump used for delivering liquefied gas, such as liquefied ammonia, liquid

hydrogen, liquid nitrogen, liquefied natural gas, liquefied ethylene gas, or liquefied petroleum gas.

Reference Signs List

[0042] 1 submersible pump

la suction inlet

lb discharge outlet 2 suction vessel

5 fluid-path switching apparatus

7 suction port 8 discharge port

11 electric motor

12 rotation shaft

14A,14B,14C bearing

15 impeller

16 pump casing

17 discharge flow passage

20 discharge pipe

22 suction valve

23 discharge valve

25 drain line

26 drain valve

31 vent line

32 vent valve

41 first flow passage

42 second flow passage

43 third flow passage

45 flow-passage structure

47 valve element

50 spring

51 valve seat

55 bypass passage

60 rotation detector

70 anti-rotation device

Claims

[Claim 1] A fluid-path switching apparatus for preventing idling rotation of a

submersible pump disposed in a suction vessel and used for delivering liquefied gas,

comprising:

a flow-passage structure having a first flow passage, a second flow passage, and

a third flow passage; and

a valve element arranged in the flow-passage structure, the valve element being

configured to allow the third flow passage to selectively communicate with either the first

flow passage or the second flow passage, the first flow passage communicating with a

discharge outlet of the submersible pump, the second flow passage communicating with

an interior of the suction vessel, and the third flow passage communicating with a

discharge port of the suction vessel.
[Claim 2] The fluid-path switching apparatus according to claim 1, wherein the

flow-passage structure further includes a bypass passage that establishes fluid

communication between the first flow passage and the third flow passage, and the bypass

passage has a cross-sectional area smaller than a cross-sectional area of the first flow

passage.
[Claim 3] The fluid-path switching apparatus according to claim 2, wherein the

cross-sectional area of the bypass passage is such that an impeller of the submersible

pump does not rotate due to flow of gas when the valve element closes the first flow

passage and the gas flows through the submersible pump and the bypass passage.
[Claim 4] The fluid-path switching apparatus according to any one of claims I to 3,

further comprising a spring configured to press the valve element against the flow

passage structure to close the first flow passage.
[Claim 5] A pump system comprising:

a submersible pump configured to deliver liquefied gas;

a suction vessel in which the submersible pump is accommodated; and

the fluid-path switching apparatus according to any one of claims 1 to 4 for

preventing idling rotation of the submersible pump.
[Claim 6] The pump system according to claim 5, further comprising a rotation

detector configured to detect rotation of the submersible pump.
[Claim 7] The pump system according to claim 5, further comprising an anti

rotation device configured to prevent rotation of the submersible pump.
[Claim 8] A method of preventing idling rotation of a submersible pump disposed

in a suction vessel and used for delivering liquefied gas, comprising:

supplying liquefied gas into the suction vessel when a first flow passage is closed

with a valve element, and a second flow passage and a third flow passage are in fluid

communication, the first flow passage communicating with a discharge outlet of the

submersible pump, the second flow passage communicating with an interior of the suction

vessel, the third flow passage communicating with a discharge port of the suction vessel;

and

delivering gas generated in the suction vessel to the discharge port through the

second flow passage and the third flow passage.
[Claim 9] The method according to claim 8, further comprising supplying purge

gas into the suction vessel before supplying the liquefied gas into the suction vessel.
[Claim 10] The method according to claim 9, wherein the purge gas is supplied into

the suction vessel through a suction port of the suction vessel and discharged through a drain line coupled to a bottom of the suction vessel, the suction port being located higher than the bottom of the suction vessel.
[Claim 11] The method according to claim 9, wherein the purge gas is supplied into

the suction vessel through a suction port of the suction vessel and discharged through the

second flow passage, the third flow passage, and the discharge port.
[Claim 12] The method according to claim 9, wherein the purge gas is supplied into

the suction vessel through a drain line coupled to a bottom of the suction vessel and

discharged through the second flow passage, the third flow passage, and the discharge

port.
[Claim 13] The method according to any one of claims 9 to 12, wherein the purge

gas is an inert gas composed of element having a boiling point lower than that of an

element constituting the liquefied gas.
[Claim 14] The method according to any one of claims 8 to 13, further comprising

operating the submersible pump in a state in which the second flow passage is closed by the valve element and the first flow passage communicates with the third flow passage.
[Claim 15] The method according to any one of claims 8 to 14, further comprising

directing gas generated in the suction vessel through the discharge port to a gas treatment

device.